Current leadframe-based plastic packages may include a die-attach material coupling the device to a metallic leadframe and allowing thermal end electrical power dissipation.
Die-attach integrity may be jeopardized as a result of the package being subjected to reliability stress tests, such as a Thermal Cycles Test (“TCT”).
Delamination may occur as a result of thermo-mechanical stresses related to different values of the Coefficient of Thermal Expansion (“CTE”) in the materials involved which may include silicon, Die Attach Material (“DAM”), copper alloy, etc.
Delamination may result in a gap being formed at the interface between two different materials in contact, such as the silicon/DAM and/or DAM/leadframe interfaces. Also, discontinuities may form within the bulk of the DAM, such as following High Temperature Storage (“HTS”) testing.
These events may be detrimental to package reliability. This may particularly be the case for packages including an exposed pad due to the integrity of the thermal/electrical path being adversely affected.
Package quality and reliability requirements are becoming more and more demanding, especially in areas such as the automotive market, where the ability to provide delamination-free packages may represent a significant factor.
Various approaches have been developed in order to counter die attach delamination, primarily focusing on improvements in materials and/or the development of new materials.
For instance, attention may be paid to leadframe finishing in various ways, including but not limited to: (1) by providing for a “roughening” treatment of the leadframe surface which may enhance mechanical adhesion to the die attach material, or (2) via deposition of organic coatings on the leadframe surface to enhance chemical adhesion to the die attach material.
The use of low-stress materials has also been proposed for the die attach material.
While certain solutions have stimulated some commercial interest, none of these can be regarded as capable of solving the issue of attach delamination in a satisfactory manner.